1. Field
One embodiment of the present invention relates to a method of forming patterns and a method of manufacturing a magnetic recording media.
2. Description of the Related Art
Due to significant progress in functions of information equipment such as personal computers in recent years, the amount of information a user deals with is significantly increasing. In such a condition, an information recording and reproducing device with a remarkably higher information density than before and a highly integrated semiconductor device are demanded. As for a hard disk drive (HDD), which is a magnetic device, there is proposed a discrete track recording media (DTR media) in which recording tracks are separated physically with a nonmagnetic material or a groove in order to improve the recording density. Because phenomena such as the side-erase phenomenon in recording and the side-read phenomenon in reproducing can be decreased in the DTR media, it is possible to increase track density, and a magnetic recording media which enables high density recording can be provided. Further, when servo information is formed together as patterns in the DTR media, there is no need to write in servo signals with a magnetic head, which requires a long period of time. On the other hand, when the servo information is not formed as designed patterns, servo tracking becomes difficult. Therefore, a finer and more accurate fabrication technique becomes necessary in order to improve the recording density.
An example of a microfabrication technique is conventional photolithography using an exposure process which enables microfabrication of a large area at once. However, it is difficult to manufacture a fine structure of 400 nm or less because it does not have resolution for a wavelength of light or less. Although examples of the microfabrication technology of a level of 400 nm or less include electron-beam lithography and focused ion beam lithography, low throughput is a problem, and further, there is a problem that the lithography device becomes expensive as miniaturization proceeds.
In contrast, nanoimprint lithography proposed by Chou et al. is inexpensive and attractive as a fabrication technique having a resolution of about 10 nm (U.S. Pat. No. 5,772,905). Chou et al. use a stamper in which patterns have been formed by electron beam lithography and reactive ion etching (RIE). First, a film of polymethyl methacrylate (PMMA), which is a thermoplastic resin, is formed on a silicon substrate as a resist. A thermal cycle nanoimprint is performed using the above-described stamper and patterns are transferred onto the resist. Residues remaining at the bottom of recesses of the resist patterns are removed with oxygen RIE to expose the surface of silicon. Then, for example, microfabrication of the substrate is performed by etching using the resist patterns as a mask, and after a film of Al and the like is formed, wiring is formed by lifting off the metal film.
Examples of an imprint method include generally a UV type imprint method (in which an ultraviolet (UV) curing resin is used), a hot embossing type imprint method, and a high pressure type imprint method at room temperature. Although the UV type enables highly precise patterns to be formed, there is a problem in the uniformity of the resist thickness because fluidity of the resist before the UV curing is high, and fluctuation of the flatness of the stamper and the substrate affect the resist thickness directly. Further, stamper has a problem that the cost is high because of its necessity to have UV-transmisivity. In the hot embossing type, distortion by contraction occurs easily because of heating, and throughput is not good due to heating and cooling steps. Further, the uniformity of the thickness is also a problem like the UV type because fluidity of the resist is high at heating.
Accordingly, considering mass-productivity and uniformity of the resist thickness, the high pressure type imprint at room temperature in which a pattern formation is performed at high pressure without heating, so that nonuniformity of thickness between the substrate and the stamper is canceled by applying a high pressure, is preferable. However, in the case of using the high pressure type imprint, there occurs a problem that the amount of the resist displaced by protrusions of the patterns and filling recesses of the patterns varies depending on the area ratio of recesses to protrusions in each pattern area of the stamper (J. Vac. Sci. Technol. B21, 98 (2003)). A DTR media has data areas including recording tracks, and servo areas including an address portion, a preamble portion and a burst portion, in which the area ratio of magnetic material is different in each area. Accordingly, the area ratio of recesses to protrusions of the pattern is different in each area of the stamper for manufacturing a DTR media. As a result, under the condition that the stamper is pushed into the resist at its maximum, difference in thickness of the resist residue remaining in recesses of the resist occurs depending on the area ratio of recesses to protrusions of the stamper.
When dispersion in the thickness of the resist residue occurs, a problem occurs when the resist residue is removed by RIE. That is, the resist residue with thin thickness is removed earlier than the resist residue with thick thickness is removed, and side-etching occurs excessively at these locations. As a result, variation in size between the patterns in the stamper and the patterns transferred onto the resist occurs. The variation in patterns size is different in each area.
Accordingly, although attempts to adjust the resist residue by changing viscosity of the resist, imprint time, and imprint temperature are performed, these methods are not effective countermeasures.